1. Field of the Invention
The present invention relates to an image forming apparatus using an electrophotographic method.
2. Description of the Related Art
Hitherto, there are known inventions relating to an image forming apparatus to which a cartridge including a developing device can be removably mounted as described in Japanese Patent Application Laid-Open Nos. 2003-215893 and S62-237477. The invention described in Japanese Patent Application Laid-Open No. 2003-215893 uses toner to which particles having a polarity opposite to a polarity of the toner are extraneously added. Further, when a toner remaining amount detecting unit detects that a toner remaining amount is a predetermined amount or less, setting of a charge and a developing bias is changed so that toner charged with reverse polarity opposite to a desired polarity is ejected from a developer container at a time of non-image formation. With this configuration, positive fog that increases just before running out of toner is suppressed so that good printed images can be obtained over a long term from an initial stage.
The invention described in Japanese Patent Application Laid-Open No. S62-237477 is an invention relating to an image forming apparatus, in which a display portion displays an indication prompting a user to shake the cartridge when it is determined that the cartridge has run out of toner based on a detection result of a remaining amount detecting sensor. Then, the cartridge is mounted again, and the toner remaining amount is detected. If it is determined again that the cartridge has run out of toner, the display portion displays an indication prompting the user to replace the cartridge.
In addition, as to detection of remaining amount of toner, it is common to indicate, for example, “Toner Low” or “Toner Out” to a user before the cartridge has completely run out of toner to cause a defective image in a printed image which a user wants to output. In other words, when “Toner Out” is indicated, the cartridge has not completely run out of toner, yet.
When “Toner Out” is indicated, the toner inside the cartridge is roughly split into two parts, including a part close to a developing roller and the other part adhering to an inner wall of a developing container. When the cartridge is replaced, these two parts of toner remain without being used.
The toner close to the developing roller is affected by history of printed images, and hence a part carried much by a surface of the developing roller and a part carried little by the surface occur. As a result, evenness of toner coating in a longitudinal direction may be deteriorated as the toner is being consumed. On the other hand, the toner adhering to the inner wall of the developing container and remaining immobile is hardly affected by charge hysteresis of a regulating member.
In this state, if the cartridge is removed and mounted again, toner inside the cartridge is vibrated because a posture of the cartridge is largely changed. As a result, it is possible to move the toner that was not moved and adhering to the inner wall of the developing container.
When the user shakes the cartridge in which a little toner remains, the user usually shakes the cartridge so that the toner moves close to the developing roller. However, the unevenness of the toner coating on the developing roller in the longitudinal direction may remain depending on the handling method.
In addition, even if the unevenness of the toner coating in the longitudinal direction is eliminated, charged state of the toner may be unstable because toner that has been constantly affected by the charge hysteresis and toner that has not been affected by the charge hysteresis are mixed on the surface of the developing roller.
When an image is printed in this state, uneven density in the longitudinal direction of the developing roller may occur in either case described above.